Gelcoat sag?

[[email protected]]

Hey guys. I've got a question regarding wing "waviness". I've got an
LS1f with very good gelcoat condition. However, if I look down the
wing long-ways, just above the leading edge I can see what looks like
a series of 4"-6" diameter lumps (for lack of a better term). They're
somewhat regularly spaced along the full length of both wings and are
parallel to the leading edge. They are very, very subtle, and you
can't really see them without looking from the correct angle to use
the glossy reflection. They're very similar on both wings and are in
the 4"-8" range up from the leading edge. I've done some "tap tests"
to see if I could detect delamination, but the wing surface is
consistently solid all over. I'm thinking this might be gelcoat "sag"
and/or just improper sanding during the last refinish. Do refinishers
have rigs to "rotate" the wings (on the spar) as they're spraying? It
almost seems like after spraying the top of the wings, they were
rotated to a position where this point of the wing was the lowest
allowing sag there. Anyone have any thoughts or comments as to what
this might be? Besides these defects, the rest of the wing surfaces
are consistently smooth and uniform.

The description of the wing refinish in the log indicates the
following:

- acrylic enamel (from previous refinish) and factory gel coat removed
via sanding
- primed with Simtec primer
- sanded with 100 grit
- primed again with Simtec primer
- sanded with 120 grit
- series of coats of Simtec white to thickness of 6-8 mils
- sanded with 180 grit
- series of coats of Simtec white to thickness of 8 mils
- wet sanded with 1000 grit
- wet sanded with 1200 grit
- wet sanded with 1500 grit
- power buffer with 3M finesse #1
- power buffer with 3M finesse #2

There's nothing in the log that refers to profiling or shaping. Only
"sanding" and "polishing". If any attempts were done to shape and/or
profile, do you think that would have been logged along with the rest
of the description? There's two and a half pages devoted to this
refinish job, so it's not like he left much out.

The ship flies beautifully, and sure seems to have good legs relative
to it's published performance numbers. I don't think these surface
defects are pronounced enough to be having any large effect on
performance, but I haven't tried any serious attempts at performance
testing either. At this time I guess I'm more interested in knowing
what they are. Although there will probably come a time when I'd like
to remedy it for the performance improvements if there are any to be
had.


Thanks,
Dave

[[email protected]]

On Dec 15, 12:42 pm, wrote:
> Hey guys. I've got a question regarding wing "waviness". I've got an
> LS1f with very good gelcoat condition. However, if I look down the
> wing long-ways, just above the leading edge I can see what looks like
> a series of 4"-6" diameter lumps (for lack of a better term). They're
> somewhat regularly spaced along the full length of both wings and are
> parallel to the leading edge. They are very, very subtle, and you
> can't really see them without looking from the correct angle to use
> the glossy reflection. They're very similar on both wings and are in
> the 4"-8" range up from the leading edge. I've done some "tap tests"
> to see if I could detect delamination, but the wing surface is
> consistently solid all over. I'm thinking this might be gelcoat "sag"
> and/or just improper sanding during the last refinish. Do refinishers
> have rigs to "rotate" the wings (on the spar) as they're spraying? It
> almost seems like after spraying the top of the wings, they were
> rotated to a position where this point of the wing was the lowest
> allowing sag there. Anyone have any thoughts or comments as to what
> this might be? Besides these defects, the rest of the wing surfaces
> are consistently smooth and uniform.
>
> The description of the wing refinish in the log indicates the
> following:
>
> - acrylic enamel (from previous refinish) and factory gel coat removed
> via sanding
> - primed with Simtec primer
> - sanded with 100 grit
> - primed again with Simtec primer
> - sanded with 120 grit
> - series of coats of Simtec white to thickness of 6-8 mils
> - sanded with 180 grit
> - series of coats of Simtec white to thickness of 8 mils
> - wet sanded with 1000 grit
> - wet sanded with 1200 grit
> - wet sanded with 1500 grit
> - power buffer with 3M finesse #1
> - power buffer with 3M finesse #2
>
> There's nothing in the log that refers to profiling or shaping. Only
> "sanding" and "polishing". If any attempts were done to shape and/or
> profile, do you think that would have been logged along with the rest
> of the description? There's two and a half pages devoted to this
> refinish job, so it's not like he left much out.
>
> The ship flies beautifully, and sure seems to have good legs relative
> to it's published performance numbers. I don't think these surface
> defects are pronounced enough to be having any large effect on
> performance, but I haven't tried any serious attempts at performance
> testing either. At this time I guess I'm more interested in knowing
> what they are. Although there will probably come a time when I'd like
> to remedy it for the performance improvements if there are any to be
> had.
>
> Thanks,
> Dave

Experienced racers have long known about the dreaded sag.
We store our wings trailing edge down over the winter and they
revert back to correct shape for the next season.
See ya, Dave

PS: RAS = Rabid Aviation Speculation ;-)

[Papa3]

On Dec 15, 12:42 pm, wrote:
> Hey guys. I've got a question regarding wing "waviness". I've got an
> LS1f with very good gelcoat condition. However, if I look down the
> wing long-ways, just above the leading edge I can see what looks like
> a series of 4"-6" diameter lumps (for lack of a better term). They're
> somewhat regularly spaced along the full length of both wings and are
> parallel to the leading edge. They are very, very subtle, and you
> can't really see them without looking from the correct angle to use
> the glossy reflection. They're very similar on both wings and are in
> the 4"-8" range up from the leading edge. I've done some "tap tests"
> to see if I could detect delamination, but the wing surface is
> consistently solid all over. I'm thinking this might be gelcoat "sag"
> and/or just improper sanding during the last refinish. Do refinishers
> have rigs to "rotate" the wings (on the spar) as they're spraying? It
> almost seems like after spraying the top of the wings, they were
> rotated to a position where this point of the wing was the lowest
> allowing sag there. Anyone have any thoughts or comments as to what
> this might be? Besides these defects, the rest of the wing surfaces
> are consistently smooth and uniform.
>
> The description of the wing refinish in the log indicates the
> following:
>
> - acrylic enamel (from previous refinish) and factory gel coat removed
> via sanding
> - primed with Simtec primer
> - sanded with 100 grit
> - primed again with Simtec primer
> - sanded with 120 grit
> - series of coats of Simtec white to thickness of 6-8 mils
> - sanded with 180 grit
> - series of coats of Simtec white to thickness of 8 mils
> - wet sanded with 1000 grit
> - wet sanded with 1200 grit
> - wet sanded with 1500 grit
> - power buffer with 3M finesse #1
> - power buffer with 3M finesse #2
>
> There's nothing in the log that refers to profiling or shaping. Only
> "sanding" and "polishing". If any attempts were done to shape and/or
> profile, do you think that would have been logged along with the rest
> of the description? There's two and a half pages devoted to this
> refinish job, so it's not like he left much out.
>
> The ship flies beautifully, and sure seems to have good legs relative
> to it's published performance numbers. I don't think these surface
> defects are pronounced enough to be having any large effect on
> performance, but I haven't tried any serious attempts at performance
> testing either. At this time I guess I'm more interested in knowing
> what they are. Although there will probably come a time when I'd like
> to remedy it for the performance improvements if there are any to be
> had.
>
> Thanks,
> Dave

Dave,

Just speculating here, but either something's missing from the logs,
your transcription of the logs is off, or ... well... something
doesn't quite make sense.

After spraying with the Simtec sandable primer, it sounds like the
refinisher sanded with 120 grit. Sounds a bit coarse to me, but
okay. Assuming it was sanded with a machined-flat bar, the wing was
probably pretty smooth at that point. Next was a coat of the white
Simtec followed by a 180 grit sanding. Okey doke. Still pretty
smooth. Next is multiple build coats of white but no sanding below
1,000 grit? Unless this guy (gal) was the best spray artist known to
man (or at least known to glider refinishing), there are bound to be
some waves introduced with multiple coats. I've never heard of
anyone NOT doing another pass with 200 grit or at least 400 grit
(followed by 600, 800) to smooth stuff out. Assuming the wing was
resting trailing edge down, I can easily see where you would get
exactly the kind of sag/ build-up you describe.

Maybe JJ or someone who did/does this for a living can chime in, but
I've never seen it done the way you describe.

BTW, if you really wanna see how bad the bumps are try this: Thin
some colored dope down to a fairly runny consistency and wipe it over
the suspect area with a paper towel. Take a piece of thin plastic
sheet and form it to the curve of the wing. Run it spanwise trying to
hold firm but consistent pressure (like you're screeding grout across
a tile). You'll be able to see the high spot/ low spot due to the
contrast.

That's my non-professional assessment.

P3

[[email protected]]

On Dec 15, 2:19 pm, wrote:
> On Dec 15, 12:42 pm, wrote:
>
>
>
>
>
> > Hey guys. I've got a question regarding wing "waviness". I've got an
> > LS1f with very good gelcoat condition. However, if I look down the
> > wing long-ways, just above the leading edge I can see what looks like
> > a series of 4"-6" diameter lumps (for lack of a better term). They're
> > somewhat regularly spaced along the full length of both wings and are
> > parallel to the leading edge. They are very, very subtle, and you
> > can't really see them without looking from the correct angle to use
> > the glossy reflection. They're very similar on both wings and are in
> > the 4"-8" range up from the leading edge. I've done some "tap tests"
> > to see if I could detect delamination, but the wing surface is
> > consistently solid all over. I'm thinking this might be gelcoat "sag"
> > and/or just improper sanding during the last refinish. Do refinishers
> > have rigs to "rotate" the wings (on the spar) as they're spraying? It
> > almost seems like after spraying the top of the wings, they were
> > rotated to a position where this point of the wing was the lowest
> > allowing sag there. Anyone have any thoughts or comments as to what
> > this might be? Besides these defects, the rest of the wing surfaces
> > are consistently smooth and uniform.
>
> > The description of the wing refinish in the log indicates the
> > following:
>
> > - acrylic enamel (from previous refinish) and factory gel coat removed
> > via sanding
> > - primed with Simtec primer
> > - sanded with 100 grit
> > - primed again with Simtec primer
> > - sanded with 120 grit
> > - series of coats of Simtec white to thickness of 6-8 mils
> > - sanded with 180 grit
> > - series of coats of Simtec white to thickness of 8 mils
> > - wet sanded with 1000 grit
> > - wet sanded with 1200 grit
> > - wet sanded with 1500 grit
> > - power buffer with 3M finesse #1
> > - power buffer with 3M finesse #2
>
> > There's nothing in the log that refers to profiling or shaping. Only
> > "sanding" and "polishing". If any attempts were done to shape and/or
> > profile, do you think that would have been logged along with the rest
> > of the description? There's two and a half pages devoted to this
> > refinish job, so it's not like he left much out.
>
> > The ship flies beautifully, and sure seems to have good legs relative
> > to it's published performance numbers. I don't think these surface
> > defects are pronounced enough to be having any large effect on
> > performance, but I haven't tried any serious attempts at performance
> > testing either. At this time I guess I'm more interested in knowing
> > what they are. Although there will probably come a time when I'd like
> > to remedy it for the performance improvements if there are any to be
> > had.
>
> > Thanks,
> > Dave
>
> Experienced racers have long known about the dreaded sag.
> We store our wings trailing edge down over the winter and they
> revert back to correct shape for the next season.
> See ya, Dave
>
> PS: RAS = Rabid Aviation Speculation ;-)- Hide quoted text -
>
> - Show quoted text -

You mean "cured" gelcoat can sag from sitting in the trailer over the
winter? That wouldn't have occurred to me. That's interesting. The
only thing that doesn't add up is that this is only in the one area on
top of the wings just behind the leading edge. Bottom of the wings are
fine. Leading edge is fine, which is the lowest point when stored.

[[email protected]]

On Dec 15, 2:57 pm, Papa3 > wrote:
> On Dec 15, 12:42 pm, wrote:
>
>
>
>
>
> > Hey guys. I've got a question regarding wing "waviness". I've got an
> > LS1f with very good gelcoat condition. However, if I look down the
> > wing long-ways, just above the leading edge I can see what looks like
> > a series of 4"-6" diameter lumps (for lack of a better term). They're
> > somewhat regularly spaced along the full length of both wings and are
> > parallel to the leading edge. They are very, very subtle, and you
> > can't really see them without looking from the correct angle to use
> > the glossy reflection. They're very similar on both wings and are in
> > the 4"-8" range up from the leading edge. I've done some "tap tests"
> > to see if I could detect delamination, but the wing surface is
> > consistently solid all over. I'm thinking this might be gelcoat "sag"
> > and/or just improper sanding during the last refinish. Do refinishers
> > have rigs to "rotate" the wings (on the spar) as they're spraying? It
> > almost seems like after spraying the top of the wings, they were
> > rotated to a position where this point of the wing was the lowest
> > allowing sag there. Anyone have any thoughts or comments as to what
> > this might be? Besides these defects, the rest of the wing surfaces
> > are consistently smooth and uniform.
>
> > The description of the wing refinish in the log indicates the
> > following:
>
> > - acrylic enamel (from previous refinish) and factory gel coat removed
> > via sanding
> > - primed with Simtec primer
> > - sanded with 100 grit
> > - primed again with Simtec primer
> > - sanded with 120 grit
> > - series of coats of Simtec white to thickness of 6-8 mils
> > - sanded with 180 grit
> > - series of coats of Simtec white to thickness of 8 mils
> > - wet sanded with 1000 grit
> > - wet sanded with 1200 grit
> > - wet sanded with 1500 grit
> > - power buffer with 3M finesse #1
> > - power buffer with 3M finesse #2
>
> > There's nothing in the log that refers to profiling or shaping. Only
> > "sanding" and "polishing". If any attempts were done to shape and/or
> > profile, do you think that would have been logged along with the rest
> > of the description? There's two and a half pages devoted to this
> > refinish job, so it's not like he left much out.
>
> > The ship flies beautifully, and sure seems to have good legs relative
> > to it's published performance numbers. I don't think these surface
> > defects are pronounced enough to be having any large effect on
> > performance, but I haven't tried any serious attempts at performance
> > testing either. At this time I guess I'm more interested in knowing
> > what they are. Although there will probably come a time when I'd like
> > to remedy it for the performance improvements if there are any to be
> > had.
>
> > Thanks,
> > Dave
>
> Dave,
>
> Just speculating here, but either something's missing from the logs,
> your transcription of the logs is off, or ... well... something
> doesn't quite make sense.
>
> After spraying with the Simtec sandable primer, it sounds like the
> refinisher sanded with 120 grit. Sounds a bit coarse to me, but
> okay. Assuming it was sanded with a machined-flat bar, the wing was
> probably pretty smooth at that point. Next was a coat of the white
> Simtec followed by a 180 grit sanding. Okey doke. Still pretty
> smooth. Next is multiple build coats of white but no sanding below
> 1,000 grit? Unless this guy (gal) was the best spray artist known to
> man (or at least known to glider refinishing), there are bound to be
> some waves introduced with multiple coats. I've never heard of
> anyone NOT doing another pass with 200 grit or at least 400 grit
> (followed by 600, 800) to smooth stuff out. Assuming the wing was
> resting trailing edge down, I can easily see where you would get
> exactly the kind of sag/ build-up you describe.
>
> Maybe JJ or someone who did/does this for a living can chime in, but
> I've never seen it done the way you describe.
>
> BTW, if you really wanna see how bad the bumps are try this: Thin
> some colored dope down to a fairly runny consistency and wipe it over
> the suspect area with a paper towel. Take a piece of thin plastic
> sheet and form it to the curve of the wing. Run it spanwise trying to
> hold firm but consistent pressure (like you're screeding grout across
> a tile). You'll be able to see the high spot/ low spot due to the
> contrast.
>
> That's my non-professional assessment.
>
> P3- Hide quoted text -
>
> - Show quoted text -

Yeah, the log is fairly explicit with the sequence of work done,
although I did summarize it. However, I looked over it again and
haven't missed anything. There definately is no mention of machined
sanding bars or such. Only the grit used for each sanding step in the
process. It's certainly possible that some details were not recorded
in the log. I may try to contact the person that did the work, but
this was in 1993. Just so happens that he was the owner at that time
and also an A&P. That might make for better memory retention since it
was his ship. We'll see.

What kind of "dope" are you referring to? The only thing that comes to
my mind is "aerogloss dope" I used to use on model planes when I was a
kid. I'm sure that's not what you're talking about

[Papa3]

On Dec 15, 5:32 pm, wrote:
> On Dec 15, 2:57 pm, Papa3 > wrote:
>
>
>
>
>
> > On Dec 15, 12:42 pm, wrote:
>
> > > Hey guys. I've got a question regarding wing "waviness". I've got an
> > > LS1f with very good gelcoat condition. However, if I look down the
> > > wing long-ways, just above the leading edge I can see what looks like
> > > a series of 4"-6" diameter lumps (for lack of a better term). They're
> > > somewhat regularly spaced along the full length of both wings and are
> > > parallel to the leading edge. They are very, very subtle, and you
> > > can't really see them without looking from the correct angle to use
> > > the glossy reflection. They're very similar on both wings and are in
> > > the 4"-8" range up from the leading edge. I've done some "tap tests"
> > > to see if I could detect delamination, but the wing surface is
> > > consistently solid all over. I'm thinking this might be gelcoat "sag"
> > > and/or just improper sanding during the last refinish. Do refinishers
> > > have rigs to "rotate" the wings (on the spar) as they're spraying? It
> > > almost seems like after spraying the top of the wings, they were
> > > rotated to a position where this point of the wing was the lowest
> > > allowing sag there. Anyone have any thoughts or comments as to what
> > > this might be? Besides these defects, the rest of the wing surfaces
> > > are consistently smooth and uniform.
>
> > > The description of the wing refinish in the log indicates the
> > > following:
>
> > > - acrylic enamel (from previous refinish) and factory gel coat removed
> > > via sanding
> > > - primed with Simtec primer
> > > - sanded with 100 grit
> > > - primed again with Simtec primer
> > > - sanded with 120 grit
> > > - series of coats of Simtec white to thickness of 6-8 mils
> > > - sanded with 180 grit
> > > - series of coats of Simtec white to thickness of 8 mils
> > > - wet sanded with 1000 grit
> > > - wet sanded with 1200 grit
> > > - wet sanded with 1500 grit
> > > - power buffer with 3M finesse #1
> > > - power buffer with 3M finesse #2
>
> > > There's nothing in the log that refers to profiling or shaping. Only
> > > "sanding" and "polishing". If any attempts were done to shape and/or
> > > profile, do you think that would have been logged along with the rest
> > > of the description? There's two and a half pages devoted to this
> > > refinish job, so it's not like he left much out.
>
> > > The ship flies beautifully, and sure seems to have good legs relative
> > > to it's published performance numbers. I don't think these surface
> > > defects are pronounced enough to be having any large effect on
> > > performance, but I haven't tried any serious attempts at performance
> > > testing either. At this time I guess I'm more interested in knowing
> > > what they are. Although there will probably come a time when I'd like
> > > to remedy it for the performance improvements if there are any to be
> > > had.
>
> > > Thanks,
> > > Dave
>
> > Dave,
>
> > Just speculating here, but either something's missing from the logs,
> > your transcription of the logs is off, or ... well... something
> > doesn't quite make sense.
>
> > After spraying with the Simtec sandable primer, it sounds like the
> > refinisher sanded with 120 grit. Sounds a bit coarse to me, but
> > okay. Assuming it was sanded with a machined-flat bar, the wing was
> > probably pretty smooth at that point. Next was a coat of the white
> > Simtec followed by a 180 grit sanding. Okey doke. Still pretty
> > smooth. Next is multiple build coats of white but no sanding below
> > 1,000 grit? Unless this guy (gal) was the best spray artist known to
> > man (or at least known to glider refinishing), there are bound to be
> > some waves introduced with multiple coats. I've never heard of
> > anyone NOT doing another pass with 200 grit or at least 400 grit
> > (followed by 600, 800) to smooth stuff out. Assuming the wing was
> > resting trailing edge down, I can easily see where you would get
> > exactly the kind of sag/ build-up you describe.
>
> > Maybe JJ or someone who did/does this for a living can chime in, but
> > I've never seen it done the way you describe.
>
> > BTW, if you really wanna see how bad the bumps are try this: Thin
> > some colored dope down to a fairly runny consistency and wipe it over
> > the suspect area with a paper towel. Take a piece of thin plastic
> > sheet and form it to the curve of the wing. Run it spanwise trying to
> > hold firm but consistent pressure (like you're screeding grout across
> > a tile). You'll be able to see the high spot/ low spot due to the
> > contrast.
>
> > That's my non-professional assessment.
>
> > P3- Hide quoted text -
>
> > - Show quoted text -
>
> Yeah, the log is fairly explicit with the sequence of work done,
> although I did summarize it. However, I looked over it again and
> haven't missed anything. There definately is no mention of machined
> sanding bars or such. Only the grit used for each sanding step in the
> process. It's certainly possible that some details were not recorded
> in the log. I may try to contact the person that did the work, but
> this was in 1993. Just so happens that he was the owner at that time
> and also an A&P. That might make for better memory retention since it
> was his ship. We'll see.
>
> What kind of "dope" are you referring to? The only thing that comes to
> my mind is "aerogloss dope" I used to use on model planes when I was a
> kid. I'm sure that's not what you're talking about- Hide quoted text -
>
> - Show quoted text -

Quick follow ups:

1. Dave Nadler was joking.
2. The sanding bar is pretty standard. Everything about the job as
described sounds first rate, so I would pretty much assume the
refinisher did it right. The only curious bit is the lack of any
further smoothing after the last round of build coats. At minimum
you usually end up with some orange peel and a few runs here and
there, and those won't come out with 1,000 grit unless there's some
magic that I don't know about.
3. Yup, aerogloss dope thinned with dope thinner.

See this great article that Ken Kochanski put together. It gives you
some context (and appreciation) of what goes into a wing refinish.
http://sailplane-racing.org/Articles/ASW20/asw20_wing.htm

[Bob Kuykendall]

In the right light, a shiny surface will show you contour disruptions
down to a handful of ten-thousandths of an inch.

If you run a waviness gage over it and get .004" or less, you've got a
lot more pressing things to worry about.

Thanks, Bob K.

[user]

Dave,

I stand mine up on end, tip down. I find this works a little better than
trailing edge down, though I think most don't have the facilities. Main
thing is that you don't let the gelcoat set in any particular position over
the winter as the low temperatures will tend to make the waves permanent.
Best of all would be a warm room (above 60F) where you have the sapce to
turn them - almost like a giant, low heat rotisserie.

Missed you at R4N. Hope you can make it in 08.



> wrote in message
...
> On Dec 15, 12:42 pm, wrote:
>> Hey guys. I've got a question regarding wing "waviness". I've got an
>> LS1f with very good gelcoat condition. However, if I look down the
>> wing long-ways, just above the leading edge I can see what looks like
>> a series of 4"-6" diameter lumps (for lack of a better term). They're
>> somewhat regularly spaced along the full length of both wings and are
>> parallel to the leading edge. They are very, very subtle, and you
>> can't really see them without looking from the correct angle to use
>> the glossy reflection. They're very similar on both wings and are in
>> the 4"-8" range up from the leading edge. I've done some "tap tests"
>> to see if I could detect delamination, but the wing surface is
>> consistently solid all over. I'm thinking this might be gelcoat "sag"
>> and/or just improper sanding during the last refinish. Do refinishers
>> have rigs to "rotate" the wings (on the spar) as they're spraying? It
>> almost seems like after spraying the top of the wings, they were
>> rotated to a position where this point of the wing was the lowest
>> allowing sag there. Anyone have any thoughts or comments as to what
>> this might be? Besides these defects, the rest of the wing surfaces
>> are consistently smooth and uniform.
>>
>> The description of the wing refinish in the log indicates the
>> following:
>>
>> - acrylic enamel (from previous refinish) and factory gel coat removed
>> via sanding
>> - primed with Simtec primer
>> - sanded with 100 grit
>> - primed again with Simtec primer
>> - sanded with 120 grit
>> - series of coats of Simtec white to thickness of 6-8 mils
>> - sanded with 180 grit
>> - series of coats of Simtec white to thickness of 8 mils
>> - wet sanded with 1000 grit
>> - wet sanded with 1200 grit
>> - wet sanded with 1500 grit
>> - power buffer with 3M finesse #1
>> - power buffer with 3M finesse #2
>>
>> There's nothing in the log that refers to profiling or shaping. Only
>> "sanding" and "polishing". If any attempts were done to shape and/or
>> profile, do you think that would have been logged along with the rest
>> of the description? There's two and a half pages devoted to this
>> refinish job, so it's not like he left much out.
>>
>> The ship flies beautifully, and sure seems to have good legs relative
>> to it's published performance numbers. I don't think these surface
>> defects are pronounced enough to be having any large effect on
>> performance, but I haven't tried any serious attempts at performance
>> testing either. At this time I guess I'm more interested in knowing
>> what they are. Although there will probably come a time when I'd like
>> to remedy it for the performance improvements if there are any to be
>> had.
>>
>> Thanks,
>> Dave
>
> Experienced racers have long known about the dreaded sag.
> We store our wings trailing edge down over the winter and they
> revert back to correct shape for the next season.
> See ya, Dave
>
> PS: RAS = Rabid Aviation Speculation ;-)

[[email protected]]

On Dec 16, 9:01 am, "user" > wrote:
> Dave,
>
> I stand mine up on end, tip down. I find this works a little better than
> trailing edge down, though I think most don't have the facilities. Main
> thing is that you don't let the gelcoat set in any particular position over
> the winter as the low temperatures will tend to make the waves permanent.
> Best of all would be a warm room (above 60F) where you have the sapce to
> turn them - almost like a giant, low heat rotisserie.
>
> Missed you at R4N. Hope you can make it in 08.
>
> > wrote in message
>
> ...
>
>
>
> > On Dec 15, 12:42 pm, wrote:
> >> Hey guys. I've got a question regarding wing "waviness". I've got an
> >> LS1f with very good gelcoat condition. However, if I look down the
> >> wing long-ways, just above the leading edge I can see what looks like
> >> a series of 4"-6" diameter lumps (for lack of a better term). They're
> >> somewhat regularly spaced along the full length of both wings and are
> >> parallel to the leading edge. They are very, very subtle, and you
> >> can't really see them without looking from the correct angle to use
> >> the glossy reflection. They're very similar on both wings and are in
> >> the 4"-8" range up from the leading edge. I've done some "tap tests"
> >> to see if I could detect delamination, but the wing surface is
> >> consistently solid all over. I'm thinking this might be gelcoat "sag"
> >> and/or just improper sanding during the last refinish. Do refinishers
> >> have rigs to "rotate" the wings (on the spar) as they're spraying? It
> >> almost seems like after spraying the top of the wings, they were
> >> rotated to a position where this point of the wing was the lowest
> >> allowing sag there. Anyone have any thoughts or comments as to what
> >> this might be? Besides these defects, the rest of the wing surfaces
> >> are consistently smooth and uniform.
>
> >> The description of the wing refinish in the log indicates the
> >> following:
>
> >> - acrylic enamel (from previous refinish) and factory gel coat removed
> >> via sanding
> >> - primed with Simtec primer
> >> - sanded with 100 grit
> >> - primed again with Simtec primer
> >> - sanded with 120 grit
> >> - series of coats of Simtec white to thickness of 6-8 mils
> >> - sanded with 180 grit
> >> - series of coats of Simtec white to thickness of 8 mils
> >> - wet sanded with 1000 grit
> >> - wet sanded with 1200 grit
> >> - wet sanded with 1500 grit
> >> - power buffer with 3M finesse #1
> >> - power buffer with 3M finesse #2
>
> >> There's nothing in the log that refers to profiling or shaping. Only
> >> "sanding" and "polishing". If any attempts were done to shape and/or
> >> profile, do you think that would have been logged along with the rest
> >> of the description? There's two and a half pages devoted to this
> >> refinish job, so it's not like he left much out.
>
> >> The ship flies beautifully, and sure seems to have good legs relative
> >> to it's published performance numbers. I don't think these surface
> >> defects are pronounced enough to be having any large effect on
> >> performance, but I haven't tried any serious attempts at performance
> >> testing either. At this time I guess I'm more interested in knowing
> >> what they are. Although there will probably come a time when I'd like
> >> to remedy it for the performance improvements if there are any to be
> >> had.
>
> >> Thanks,
> >> Dave
>
> > Experienced racers have long known about the dreaded sag.
> > We store our wings trailing edge down over the winter and they
> > revert back to correct shape for the next season.
> > See ya, Dave
>
> > PS: RAS = Rabid Aviation Speculation ;-)- Hide quoted text -
>
> - Show quoted text -

That's just mean! LOL!

[Andy[_1_]]

On Dec 15, 1:19 pm, wrote:

> Experienced racers have long known about the dreaded sag.


I know this reply was in jest but at Hobbs years ago I got into
conversation with a DG owner. I forget who it was or what the glider
type was. He told me that the gell coat on his wings had sagged. He
also told me the factory had told him it was due to being stored in
the trailer above a maximum temperature approved by the factory. He
seemed upset enough about the problem that I assumed it was true. I
have never heard of this happening to anyone else and don't pretend
to understand the physics that could allow it to happen.

Andy

[Martin Gregorie[_1_]]

Andy wrote:
> On Dec 15, 1:19 pm, wrote:
>
>> Experienced racers have long known about the dreaded sag.
>
>
> I know this reply was in jest but at Hobbs years ago I got into
> conversation with a DG owner. I forget who it was or what the glider
> type was. He told me that the gell coat on his wings had sagged. He
> also told me the factory had told him it was due to being stored in
> the trailer above a maximum temperature approved by the factory. He
> seemed upset enough about the problem that I assumed it was true. I
> have never heard of this happening to anyone else and don't pretend
> to understand the physics that could allow it to happen.
>
Way back when the CIBA-Geigy 24 hour Araldite was a new wonder glue,
i.e. the mid 60s, we soon discovered that it had to be cured at or above
the design operating temperature for the completed assembly. If you
cured it at a lower temperature the epoxy would soften when its
temperature was raised above the cure temperature, even if this was
quite some time after the glue had set up.

I have no knowledge whether this applied to other contemporary epoxies
by CIBA-Geigy and other manufacturers, except that the Standard Libelle
Owners Manual (which was written around the same time), says explicitly
that storing the glider in a hot trailer will not warp or soften it
provided that the parts are not under stress. It adds that this will
"temper" the structure, which may even increase its strength slightly.

HTH


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |